Apparatus for cracking heavy hydrocarbons to produce lighter hydrocarbons



E. W. ISOM June 5, 1934.

APPARATUS FOR CRACKING HEAVY HYDROCARBONS TO PRODUCE LIGHTERHYDROCARBONS Original Filed Aug. 28, 1922 INVENTOR BY XT FORNEYSPatented June 5, 1934 UNITED STATES APPARATUS FOR CRACKING HEAVY HY-DROCARBONS TO HYDRO CARBON S PRODUCE LIGHTER Edward W. Isom, Scarsdale,N. Y., assignor to Sinclair Refining Company, Chicago, 111., acorporation of Maine Original application August 28, 1922, Serial No.

584,711. Divided and this application June 10, 1927, Serial No. 197,781

3 Claims.

In the process commonly employed for converting higher into lowerhydrocarbons, more particularly for converting gas oil and the like intogasoline, a body of the heavy hydrocarbon is distilled under suchpressure that its temperature is raised in the liquid phase to a pointat which the hydrocarbons composing the oil, or part of them, aredecomposed to lower or lighter hydrocarbons. Another known process forconverting higher into lower hydrocarbons is to crack the hydrocarbonsin the vapor phase by first converting them into vapors and thensubjecting them while in that state to the cracking temperaure.

The present invention relates to a new and improved apparatus forcracking heavier oils, for the manufacture of gasoline, etc., in which apart of the oil is cracked in the vapor phase and a part in the liquidphase, and in which the vapor phase and liquid phase cracking operationsare combined in a particularly advantageous manner. The preferred methodof operation of the apparatus of the present invention involves crackinga part of the oil in the vapor phase and introducing the resultingproducts of the vapor phase cracking operation directly into a pressurestill containing a body of oil maintained at a cracking temperature andpressure. By introducing the products of the vapor phase crackingoperation into the-liquid phase cracking still in this way, the productsof the vapor phase cracking operation are caused to comzningle andcombine with the liquid and gaseous or vaporous products in the liquidphase still, and the products of the vapor phase cracking are thussubjected to the cracking conditions prevailing in the liquid phasestill. The heavier or less volatile products of the vapor phase crackingoperation become admixed with the charge in the liquid phase still,while the gases and lighter vapors from the vapor phase crackingoperation commingle with the gaseous and vaporized products in theliquid phase still and, to a greater or less extent, appear to reactor'combine with such products.

This application is a division of my application filed August 28, 1922,Serial No. 534,711.

According to one desirable method of operating the apparatus of theinvention the vapor phase cracking operation is carried out at a muchhigher temperature than that required for the liquid phase crackingoperation, and the superheated products from the vapor phase crackingoperation are introduced into the body of oil in the liquid phasepressure still, thereby heating it internally. For example, the vaporphase crackheating this body of oil and being themselves cooled to thetemperature prevailing in the liquid phase pressure still which may be,for example, a temperature of 700 to 750 F. By combining a hightemperature vapor phase cracking operation in this way with theoperation of a liquid phase pressure still, the charge in the pressurestill can be heated internally to the cracking temperature, the chargeof the pressure still being cracked at a considerably lower temperaturethan that used in the vapor phase cracking operation. The entire heatingof the liquid phase still can be supplied internally by the highlysuperheated vaporous product from the vapor phase cracking operation,thus avoiding the application of external heat to the still walls andpreventing the formation of carbon deposits thereon and making possiblethe treatment of heavy oils and residues, and the reduction of theseheavy oils and residues to a heavy sludge or even to coke. Instead ofintroducing the vapors from the vapor phase crackingoperation into thebody of liquid in the liquid phase still, they may be introduced intothe vapors in the vapor space of the still, thus heating the vapors inthe still and being themselves cooled. Interaction between the admixedvaporous products is thus promoted. Or a part of the products from thevapor phase cracking operation can be introduced into the liquid body inthe pressure still and a part into the vapor space above the body ofliquid.

The vapor phase cracking operation can be carried out in diiierentcracking apparatus and under different conditions. In the operation ofthe combined apparatus of the present invention, however, it isparticularly advantageous to utilize, in the vapor phase crackingoperation, the kerosene and lighter gas oil fractions which are notreadily cracked, except at high pressures, in a liquid state. Such oilscan be readily vaporized and can be subjected to the necessary crackingtemperature without excessive c'arbon formation. 7 The'crackingoperation can readily be carried out, for example, in externally heatedcoils throughwhich the oil vapors are passed ata high velocity andbrought to the cracking temperature, e. g. around 1000 F. The vapors,forex,-

ample, of kerosene or light gas oil, can be sub- -jected to crackingwithout admixture of other gases or vapors, or the oil vapors may beadmixed with a greater or less amount of steam or of the permanent gasresulting from the combined cracking operations, or with other suitablegases. The pressure maintained in the vapor phase cracking apparatus canbe varied but, in general, it should be as high or higher than thatmaintained in the pressure still so that the pressure will be sufficientto force the cracked products into the pressure still. Where a long pipecoil or series of coils is used in the vapor phase cracking operation, aconsiderably higher pressure may be necessary at the feed end of thecoil to overcome the frictional resistance of the oil and oil vaporsthrough the coils. Where the pressure maintained in the pressure stillis around 60 to 100 lbs. asufiiciently higher pressure should bemaintained in the vapor phase cracking system to insure the discharge ofthe products thereof into the liquid phase pressure still.

The temperature as well as the pressure, in the vapor phase crackingsystem, can be varied. For example, by using a higher. temperature, anincreased amount of aromatic hydrocarbons, such as benzol and toluol,can be produced by the vapor phase cracking operation. A temperature ofaround 1100 F. anda pressure in excess of 60 lbs. can thus be used, forexample, where an increased amount of aromatic hydrocarbons is desiredin the final motor fuel or gasoline produced by the combined crackingoperations.

The liquid phase cracking operation carried out in the pressure still islikewise capable of considerable variation; and different constructionsof pressure stills can be used. Where the products fromthe vapor phasecracking operation are introduced into the body of oil in the pressurestill, they will cause agitation of this oil, and, where they are at amuch higher temperature they will heat the body of oil internally, andthe heavier products from the vapor phase cracking operation will becomeadmixed with the charge in the still while the gases and lighter vapors,will admix with the vapors formed in the pressure still and theresulting lighter vapors, after such further reaction as may take place,will escape from the pressure still as a composite distillate. Theintroduction of the vapor phase products into the liquid phase pressurestill, and the heating of the oil internally by such products, enablesthe cracking operation to be carried out at a lower temperature andpressure than when the oil is heated externally.

The temperature and pressure in the pressure still can be varied. Apressure of around to lbs. and a corresponding. temperature, can thus beemployed, or the operation can be carried out at a lower temperature andpressure, for example, from 60 to 90 lbs. as well as at higher pressuresof lbs. or more. The charge in the pressure still will have added to itthe heavier products from the vapor phase cracking operation, and theseheavier products will then be subjected to further cracking.

The advantages of the invention will be further described andillustrated in connection with the accompanying drawing whichillustates, in a somewhat conventional and diagrammatic manner, one formof apparatus embodying the invention. It is to be understood, however,that the specific disclosure is for the purpose of illustration andexemplification and that the scope of the invention is not limitedthereto but is defined in the following claims in which I haveendeavored to distinguish it from the prior art so far as known to me,without, however, relinquishing or abandoning any portion or featurethereof.

The liquid phase still 55 shown in the drawing is the ordinary shellform of still. A furnace 56 is provided for assisting in heating the oilto start the process or to overcome the radiation losses or as anauxiliary to the main heating of the oil internally. During the mainoperation of the process this furnace 56 may not be used or may be usedonly to a suflicient extent to prevent undue radiation losses, theinternal heating of the coil being relied upon for carrying out thecracking operation.

The vapors resulting from the combined cracking operation escape throughthe pipe 57 which may be provided with a pressure reducing valve (notshown) and then pass to the exchanger 12 where a portion of the vaporsis condensed. When this exchanger acts as a reflux tower the condensatereturns to the still through the pipes '70 and 58 and enters the body ofoil through the perforated pipe 59. Instead of refluxing the condensateto the still it may be drawn ofi through the branch connection 69 to thereservoir 19 for admixture with the condensate from the exchanger isflowing to the reservoir through pipe 18 or it may be drawn off to aseparate reservoir (not shown). The vapors from the exchanger 12 escapeby pipe 15 to a second exchanger 16 where a further portion of thevapors is condensed. When liquid condensate is body, by the vaporsdischarged from the vapor phase cracking apparatus through the pipes 60and 63, the pipe 63 being a perforated pipe for distributing the vaporsand bringing them into intimate contact with the oil. A check valve 61and hand-valve 62 for controlling or assisting in controlling the flowof cracked vapors are provided in the pipe 60. A tar draw-off from thestill 55 is indicated at 6'7 and may be used when the process is carriedout as a continuous process. This tar draw off is not used when thecharge is run down to coke.

The illustration of apparatus for carrying out the vapor-phase crackingoperation is more or less conventional and diagrammatic, but in practiceit will be understood that a sufiicient number or length of pipes willbe used in the coil or coils 23 to insure vaporizing the oil andsubjecting it to the necessary. temperature for effecting the vaporphase cracking to a greater or less extent of the oil. When valve 62 isopen, the products from the vapor phase cracking operation, if

under a pressure somewhat in excess of that in the pressure still, willbe forced into the pressure still. The pressure in the vapor phasecracking coil, in such a case, would be controlled by the pressure onthe liquid phase still and the rate of feed to the vapor phase crackingcoil. The specific form and construction of the furnace employed, aswell as the size and number of the pipes employed, in the vapor phasecracking apparatus can be varied, but in the form shown the furnace isheated by a burner 29 and the products of combustion pass ina zig-zagcourse and leave the furnace through a stack flue 30 at the bottom.

In order to assist inmaintaining a uniform furnace temperature,arrangement is made for recirculating a greater or less amount of thegases from near the exit of the furnace and reintroducing them so thatthey become admixed with the fresh products of combustion from thefirebox 24. A return flue 31 is shown in the drawing leading from nearthe exit to a point near the inlet and provided with an injector for=forcing the recirculation of the products of combustion to a greater orless extent. The hot products of combustion are thus diluted with therecirculated cooler products of combustion. By regulatingthe amount ofgases recirculated and the heat supplied to the furnace by the burner,it is possible to obtain a uniform and definite temperature, forexample, a temperature of around 1000 F. at the exit of the crackingcoils.

The vapor phase cracking apparatus may be supplied with the intermediateor kerosene condensate from the reservoir 19 by means of pipe 20 or withcharging stock of a similar character from the supply tank 44. The freshstock for the liquid phase cracking operation, e. g., gas oil, can besupplied from the reservoir or supply tank 34 and employed to assist incondensing the vapors in exchangers l2 and 16 being thereby preheated.This preheated oil can then be supplied through the pipe 64 tothe pipes58 and 59, and thus introduced into the body of oil in the still. Acheck-valve 65 and hand-valve 66 are provided in the pipe at theconnection between the pipe 64 and the pipe 58. Meters are shown at 37and 46. The fresh oil thus fed to the still is mingled with any refluxand the two are introduced into the oil together. The vapor phasecracking apparatus is supplied with oil by means of the pump 21 and pipe22 at a pressure sufficient to force the resulting products, afterhaving been subjected to the vapor phase cracking operation, into themain body of oil in the still 55. These products from the vapor phasecracking apparatus pass through the tar separator 26 and thence throughthe pipes 60 and 63 into the still in the manner above described.

The lightest portion of the vapors, which is uncondensed in theexchangers 12 and 16 and which contains the desired cracked distillateor pressure distillate, escapes by pipe 17 to any desired form of finalcondenser. As these condensers are common and well known it is notconsiderednecessary to illustrate them. A pressure reducing valve may beprovided in the pipe 57 to permit the exchangers 12 and 16 to beoperated at approximately atmospheric pressure, while, by opening thisvalve and regulating the pressure by the valve in the pipe 17 theexchangers 12 and 16 can be kept at the same pressure as that maintainedin the still, while the final condenser can be kept at substantiallyatmospheric pressure; or by regulating the pressure at the outlet of thefinal condenser, the final condensation can be carried out underpressure.

- In the operation of the combined apparatus illustrated, the still 55is charged with the oil, such as gas oil, which is to be subjected tothe liquid phase cracking operation. This oil may be heated before itenters the still or it may be heated in the still to a temperatureapproximating that at which cracking takes place. The furnace 56 may beused in this preheating operation. The kerosene or other oil in thereservoir 19 or in the supply tank 44 is then forced through the .to agreater or less extent.

vapor phase cracking coil where it is subjected to a crackingtemperature and where cracking takes place to a greater or less extent.The resulting cracked vapors may thus be heated to a temperature around1000 F. under a pressure in excess of that maintained in the pressurestill 55 and then discharged into the body of oil. The highlysuperheated vapors are thus cooled to approxi- -mately the temperatureof the oil while the oil is in turn heated. The heavier products fromthe vapor phase cracking operation are added to the body 05 liquid oilwhile the lighter vapors and gases commingle with the vapors and gasesfrom the liquid phase cracking operation. The liquid phase crackingoperation is thus carried out with effective internal heating of thebody of oil and with the production of a resulting distillate of acomposite character containing the lighter products from the vapor phasecracking operation as well as the lighter products from the liquid phasecracking operation, together with such further amounts of light vaporsas may result from the reaction of the admixed gases and vapors.

The lighter products produced by the cracking of oil in the vapor phasecontain a considerable amount of unsaturated compounds and have arelatively high iodine value. The composite product of the combinedliquid phase and vapor phase cracking operation has a much lower iodinevalue than the vapor phase product and is comparable with that obtainedin liquid phase cracking operations carried out under pressure. Theamount of permanent gas formed in the vapor phase cracking of oil isgenerally much higher than that with liquid phase cracking underpressure, but the amount of gas formed by the combined process iscomparable with that obtained by straight pressure distillation. It is;probable therefore that a considerable amount of reaction takes placebetween the products of the vapor phase cracking operation and those ofthe liquid phase cracking operation whereby the permanent gases andlighter vapors react with each other The cooling of the highlysuperheated vapors from the vapor phase cracking operation, byintroducing them into the body of liquid, prevents further objectionableovercracking. For example, the superheated vapors which are heated inthe vapor phase cracking coils to around 1000 F. will be cooled to aconsiderably lower temperature, e. g., around WOO-750 F. when they arebrought into intimate contact with the body of liquid oil. By carryingout the vapor phase cracking process in this way bringing the vapors upto the superheated stage necessary for cracking, and then almostimmediately stopping the reaction by introducing them into a mass ofcooler oil, the further over"-' cracking with resulting formation of anincreased amount of unsaturated compounds is prevented. The portion ofthe vapor phase products which is condensed when subjected to thiscooling effect is then further subjected to the liquid phase crackingconditions, and such portions as can be further cracked in this way aresubjected to the cracking operation along with the liquid charged intothe pressure still; while such fractions as are not readily treated inthe pressure still and as are not desired in the final distillate can bereturned to the vapor phase cracking process.

The respective portions of the cracked products which can best betreated in the vapor phase and in the liquid phase cracking operationscan thus be treated in these respective operations,

the lighter fractions too heavy for the final dil- 5 tillate, beingrecycled repeatedly through the vapor phase cracking coil where thevapors are heated to high temperatures for comparatively short periods,and the lighter fractions are thus progressively cracked into productswhich finally leave the combined operations as the desired distillate oras permanent gas or residue. This recycling of the lighter fractions(for example, those corresponding generally to kerosene or light gas oiland which are not readily cracked in a pressure still except at highpressures) makes it possible to subject them repeatedly to a crackingtemperature in the vapor phase, with partial cracking of the vapors,.and with avoidance of prolonged exposure and overcracking at elevatedtemperatures, the vapors being heated to the cracking temperature forcomparatively short periods and being then cooled by introduction intothe body of liquid oil at a lower temperature. The separation orthelighter or intermediate fractions so that they are not returned to thepressure still also makes for more efficient operation of this still,since the heavier oils can be more readily cracked, and at a lowerpressure; while the lighter fractions are those most advantageouslytreated in the vapor phase.

Where it is desired to subject a portion of the heavier condensate fromthe pressure. still to cracking in the vapor phase this can beaccomplished by closing the valve in the pipe '70 so as to preventrefluxing of the heavier oil to the still and opening the valve in thepipe 69 so that the heavier condensate from the exchanger 12 will passto the reservoir 19. In this way the heavier and lighter fractions canbe combined for treatment in the vapor phase.

In referring to the heavier and lighter fractions of the condensedvapors it will of course be understood that the final condensate will bethe desired cracked distillate or pressure distillate and will containthe gasoline; the lighter and heavier condensates referred to being thefractions which are separated from the vapors before they are subjectedto the final condensation.

In the operation of the apparatus illustrated,

the running of the charge to dryness can be carried out with shuttingofi" of the feed by closing the valve 66 in the pipe 58 and opening thevalve in the pipe 68 which will lead the preheated oil to another stillor to a place of storage. The refluxing of the heavier condensed vaporsback to the still through the pipes 58 and 59 can also be discontinuedby closing the valve in the pipe 70 and the condensed vapors can then beled to the receptacle 19 by opening the valve in the pipe 69. When thestill is operated in this way the cracking operation will continuewithout the introduction of further amounts of oil until the cracking ofthe residue constituents has been carried to completion or to thedesired point. Inasmuch as the walls of the still are not heatedexternally to high temperatures, the coke or coke-like residue remainingin the still at the end of the operation will be relatively easy toremove.

I claim:

1. An apparatus for treating hydrocarbon oil, comprising a heating coildisposed within a furnace, an enlarged reaction chamber, meansconnecting said coil with such chamber, a dephlegmator, means forconveying vapors from said enlarged chamber to said dephlegmator, meansfor introducing oil to said dephlegmator to act as a dephlegmatingmedium for the vapors therein, a conduit for conveying reflux condensatefrom said dephlegmator to said enlarged reaction chamber, a valve insaid conduit, a second conduit for conveying the reflux condensatedirectly to the heating coil when said valve is closed, and means formaintaining a self-generated superatmospheric pressure on the oilundergoing conversion in the apparatus.

2. An apparatus for treating hydrocarbon oil, comprising a single-passheating coil disposed within a furnace, an enlarged reaction chamber,means connecting said coil with such chamber,

a dephlegmator, means for conveying vapors from said enlarged chamber tosaid dephlegmator, means for passing relatively cool oil in indirectheat exchanging relation with the vapors in said dephlegmator to act asa cooling and dephlegmating medium for the vapors therein, a conduit forconveying reflux condensate from said dephlegmator to said enlargedreaction chamher, a valve in said conduit, a second conduit forconveying the reflux condensate directly to the heating coil when saidvalve is closed and means for maintaining a self-generatedsuperatmospheric pressure on the oil undergoing conversion in theapparatus;

3. An apparatus for converting high boiling hydrocarbon oils into lowerboiling products in combined vapor-liquid phase, in combination, asingle pass heating coil adapted for cracking oil under pressure andhigh temperature in the vapor phase, an unheated still, means forsupplying oil under pressure thereto, means for delivering the highlyheated evolved vapors from the vapor phase converting means into thebody of oil in said still to raise and maintain the oil at a temperaturesumcient for liquid phase conversion, means for removing from the stillthe vapors evolved by the combined vapor liquid phase operation and forconveying the vapor mixture to a dephlegmator, means for passingrelatively cool oil in heat exchanging relation with the vapors in saiddephlegmator to act as a cooling and dephlegmating medium for the Vaporstherein, and means for conveying condensate from said dephlegmator forretreatment to both the vapor phase cracking means and to the still,including means for controlling the relative proportions of saidcondensate to be re-' 1 rid

